Chain saw with cyclically restricted and continuously vented acoustic filtering

ABSTRACT

A chain saw including a noise suppressing apparatus wherein a pulsing exhaust flow is passed through an acoustic filter and is cyclically restricted while permitting a continuous venting of at least a portion of the exhaust flow. Method and apparatus for effecting noise reduction of chain saws and engines wherein an expansion chamber, acoustic filter means, and cyclic flow restriction and continuous venting means coact to effect noise reduction. Method and apparatus for effecting noise reduction of chain saws and engines wherein a free &#39;&#39;&#39;&#39;floating&#39;&#39;&#39;&#39; or unbiased, cyclically operable flow restricting means is employed.

United States Patent [191 Bailey CHAIN SAW WITH CYCLICALLY RESTRICTEDAND CONTINUOUSLY VENTED ACOUSTIC FILTERING [75] Inventor: Jay RichardBailey, Chatsworth,

Calif.

[73] Assignee: McCulloch Corporation, Los

Angeles, Calif.

[22] Filed: Jan. 18, 1974 [21] Appl. No.: 434,654

Related US. Application Data [63] Continuation-in-part of Ser. No.220,632, Jan. 25,

1972, Pat. NO. 3,798,769.

[52] U.S. Cl. 30/381; 18l/64 R [51] Int. Cl. B27B 17/00; FOIN 1/16 [58]Field of Search 30/381, 383; 181/36, 40, 181/57, 58, 64 B, 64 R, 64 A;l73/DIG. 2

[56] References Cited UNITED STATES PATENTS 2,214,894 9/1940 Wilson181/64 B 3,106,985 10/1953 Recupito 181/36 R 5H0 f h m0 702 L 509 ,6182"5||b 502 L Nov. 25, 1975 Miller l8l/40 Nelson l8l/58 Primary ExaminerAlLawrence Smith Assistant ExaminerJ. C. Peters Attorney, Agent, orFirmBurns, Doane, Swecker & Mathis [57] ABSTRACT A chain saw including anoise suppressing apparatus wherein a pulsing exhaust flow is passedthrough an acoustic filter and is cyclically restricted while permittinga continuous venting of at least a portion of the exhaust flow.

Method and apparatus for effecting noise reduction of chain saws andengines wherein an expansion chamber, acoustic filter means, and cyclicflow restriction and continuous venting means coact to effect noisereduction.

Method and apparatus for effecting noise reduction of chain saws andengines wherein a free floating or unbiased, cyclically operable flowrestricting means is employed.

8 Claims, 12 Drawing Figures U. S. Patent Nov. 25, 1975 Sheet 1,0f33,921,290

U.S I"Patent Nov.25, 1975 Sheet3 0f3 3,921,290

INLET EXPANSION BAFFLE CYCLIC RESTRICTION AND VENTING DEFLECTIONDISCHARGE FIG. l2

' CHAIN SAW WITH CYCLICALLY RESTRICTED AND CONTINUOUSLY VENTED ACOUSTICFILTERING RELATED APPLICATION This application is a continuation in partof my prior and copending application Ser. No. 220,632 filed Jan. 25,l972, and entitled Apparatus for Reducing the Operating Noise of a ChainSaw, now U.S. Pat. No. 3,798,769.

The entire disclosure of this aforesaid copending application isincorporated by reference insofar as it relates to the claimed and/ordisclosed subject matter of the present application.

GENERAL BACKGROUND, OBJECTS AND SUMMARY OF lNVENTlON With the-increasingsocietal emphasis upon ecological improvements, those dealing withcyclically operable internal combustion engines which are operated inpublic areas, or in the vicinity of workmen, have been subjected toincreasing pressure to reduce the noise output of such engines and theirassociated components.

Particularly in the chain saw art has there been a continuinglyintensified need to reduce the, at times, annoying noise characteristicsof chain saw engines.

As is noted in the aforesaid copending application Ser. No. 220,632, agreat deal of magic or art as opposed to predictable engineering isinvolved in ascertaining those combinations of noise suppressingtechniques which will most effectively reduce the operating noise chainsaws while maintaining an acceptable power output. v

As a part of the design dilemma facing those practicing in the chain sawart, it is desired to effect a reduction in the operating noise of chainsaw engines during the medium and/or heavy cutting? operating range ofchain saw engine speeds (i.e., on the-order of 6,000 to 7,000 rpm) wheremedium and/or heavy cutting are involved, while'minimizing the powerloss of the generally small horsepower rated engines conventionally usedin chain saws.

As will be recognized, at higher engine-speeds, such as thoseencountered during limbing operations, a significantly lower powerrequirement is imposed on the chain saw such that at these higher enginespeeds a greater sacrifice of power can be tolerated in order to producean acceptable reduction in noise level.

Taking these factors into consideration, it is an object of the presentinvention to advance the art by providing an improved noise suppressingtechnique having particular utility in the chain saw art which willeffectively dissipate the noise producing energy of a chain saw engineexhaust over periods of time so as to reduce noise intensity andminimize the irritating crack type of noise often associated with chainsaw operation.

It is a further object of the invention to effect such noise suppressionin a unique manner soas to maintain an effective power level,particularly at the relatively low and/or median rpm levels of engineoperation where heavy and/or medium load cutting are involved, whilemaintaining an acceptable or minimal reduction in power due to noisesuppression.

A further object of the invention is to accomplish the hertofore statedobjectives with respect to noise suppression and maintenance ofeffective engine power side in a technique characterized by thefollowing method steps.

This method aspect involves a method for reducing the operating noise ofa chain saw which includes chain saw cutting means including guide barmeans, and cutter chain means supported on the guide bar means fortraversal through a cutting path. The chain saw further includes chainsaw power means including chain saw engine means having a workingchamber means, and chain saw power transmitting means operable totransmit driving force to said cutter chain means and cause said cutterchain means to traverse said cutting path.

The inventive aspects of this method reside in cooperative stepsincluding the provision of exhaust passage means communicating with theworking chamber means of the chain saw engine means and transmitting aflow of cyclically pulsing exhaust gas from the working chamber meansthrough the exhaust passage means. This flow of exhaust gasis cyclicallyrestricted. A flow of at least a portion of this flow of exhaust gasthrough the exhaust passage means is continuously vented to theatmosphere. In this method aspect, the cyclic restricting of the flow ofexhaust gas is caused to occur through the unimpeded, cycling action ofa free floating, flow restricting element.

Another independently significant method aspect of the invention entailsthe following combination of method steps.

This method relates to the reducing of the operating noise of a chainsaw, which chain saw includes chain saw cutting means having guide barmeans, and cutter chain means supported on the guide bar means fortraversal through a cutting path. The chain saw further includes chainsaw power means including chain saw engine means having a workingchamber means, and chain saw power transmitting means operable totransmit driving force to the cutter chain means and cause the cutterchain means to traverse the cutting path. Inventive aspects of thismethod reside in steps initiated by the provision of exhaust passagemeans communicating with the working chamber means of the chain sawengine means and transmitting a flow of cyclically pulsing exhaust gasfrom the working chamber means through this exhaust passage means. Thisflow of exhaust gas is passed into surge chamber means, with the flowbeing operable to expand therewithin. Acoustic filter means are providedincluding generally tubular means including lateral wall means defininginterior passage means communicating with the atmosphere and extendingwithin the surge chamber means. This acoustic filter means furtherincludes transverse passage means intersecting the lateral wall means ofthe generally tubular means and providing restricted, acousticfiltering, fluid communication between the surge chamber means and theinterior passage means of the generally tubular means. The flow ofexhaust gas is acoustically filtered by passing the flow from the surgechamber means through the acoustic filter means. At least a portion ofthe flow of exhaust gas passing through said acoustic filter means iscyclically restricted and a portion of the flow of exhaust gas totheatmosphere is continuously vented.

Particularly significant facets of the invention reside in uniquelyinteracting novel combinations of apparatus means operable tocooperatively implement either or both of the foregoing method concepts.

Broader aspects of the invention reside in the application of theforegoing method and apparatus concepts to noise suppression ofcyclically operable internal combustion engines in a general sense.

More specific apparatus aspects of the invention entail the followingcombination, implemented in the context of the foregoing discussion.

In these more specificapparatus aspects, the flow restricting means istelescopingly associated with the tubular means and is supported by thenoise reducing apparatus for substantially unimpeded reciprocatingmovement relative to the tubular means. The flow restricting meansincludes wall means telescopingly associated with the tubular means andis operable to cooperate with such lateral wall means and interiorpassage means of said tubular means to define generally annular passagemeans within the interior passage means. The continuously operableventing means comprises generally central venting passage meansextending generally centrally and longitudinally of each of the flowrestricting means and the annular passage means, with the ventingpassage means being defined by and carried by the flow restrictingmeans. The generally annular passage means provides fluid communicationbetween the generally central. venting passage means and the surgechamber means. The generally annular passage means is operable toprovide fluid communication, independent of the generally centralventing passage means, between the atmosphere and the surge chambermeans. The flow restricting means includes generally annular, flowrestricting wall means extending transversely of the generally annularpassage means, which annular wall means is cyclically operable inresponse to the flow of exhaust gas to cyclically restrict a portion ofthe annular passage means communicating with the atmosphere. Thisgenerally annular wall means is opera- DRAWINGS Preferred embodiments ofthe present invention are illustrated in the appended drawings in which:

FIG. 1 provides a fragmentary, perspective view of a representativechain saw in which a preferred noise suppressing apparatus of thepresent invention is incorporated;

FIG. 2 provides an enlarged, exploded, perspective view of disassembledcomponents of a preferred noise suppressing apparatus incorporated inthe FIG. 1 chain saw; 7

FIG. 3 provides a still further enlarged sectional view of the FIG. 2noise suppressing apparatus as viewed generally along section line 3-3of FIG. 2;

FIG. 4 provides an enlarged sectional view of the FIG. 2 noisesuppressing apparatus as viewed along section line 4-4 of FIG. 2;

FIG. 5 provides a still further enlarged, transverse, sectional view'ofthe FIG. 2 noise suppressing apparatus as viewed generally along sectionline 55;

FIG. 6 provides an elevational sectional view of the cyclically operableflow restricting mechanism illustrated in perspective view in FIG. 2;

FIG. 7 provides a transverse sectional viewof the FIGS. 2 and 6 exhaustflow restricting means as viewed along section line 7-7 of FIG. 6;

FIG. 8 provides a sectioned, elevational view of a first alternativeform of a flow restricting mechanism which may be employed in lieu ofthe FIG. 6 device;

FIG. 9 provides a transverse sectional view of the alternative flowrestricting embodiment shown in FIG. 8, as viewed along section line 9-9of FIG. 8;

FIG. 10 illustrates in a sectional, elevational format, a still furtheralternative embodiment of a cyclically operable exhaust flow restrictingmechanism which also may be employed in lieu of the mechanism shown inFIGS. 2 and 6; I

FIG. 11 provides a transverse sectional view of the FIG. 10 flowrestricting device, as viewed along section line ll11 of FIG. 10; and IFIG. 12 provides, in a schematic format, an illustration of uniquelycooperating noise suppressing techniques which are believed tosynergistically interact and produce improved noise suppressingtechniques, particularly in the environment of a chain saw, asapplicable to apparatus shown in FIGS. 1 through 11.

Having described the subject matter of the appended drawings, it is nowappropriate to consider a representative chain saw context of theinvention along with structural details of the improved noisesuppressing apparatus and method of the present invention;

DETAILED DESCRIPTION OF INVENTION Representative Chain Saw Context ofInvention FIG. 1 illustrates a representative 'chain saw 1, including amuffler ornoisesuppressing apparatus 2 fabricated in accordance with anyof several embodiments of the present invention.

Chain saw 1 includes a guide bar 101. A cutter chain 102 is slidablysupported on the periphery of the guide bar 101 for movement through acutting plane defining a cutting path. This cutting plane may beconsidered to comprise a longitudinally extending, upright median planecoextensive with the generally ovate cutter chain configuration.

Chain saw '1 comprises an engine-assembly 103 including a piston andcylinder means 104. As shown in FIG. 1, a cylinder or working chambercomponent of the piston and cylinder assembly 104 may be oriented sothat the axis of reciprocation of the piston longitudinally of the guidebar 101 and the aforesaid cutting plane.

A crankshaft means 106, including the external housing 107 shown in FIG.1, is operated in a manner now well understood to translatereciprocating movement of the piston of the engine assembly 103 intorotary movement of a sprocket wheel which is disposed in drivingengagement with a cutter chain 102.

This crankshaft is mounted for rotation about an axis of crankshaftrotation 108 which extends generally perpendicular to the aforesaidcutting plane, Le, a planar extension of the longitudinal upright medianplane of the guide bar 101.

With this arrangement, the chain saw 1 will generate vibrationsprincipally aligned with a plane extending generally parallel to orlongitudinally of the aforesaid cutting plane. As a consequence, theaxis of crankshaft rotation 108 may be deemed to pass generallyperpendicular to this principal vibration plane.

In describing the various preferred embodiments of the muffler 2,reference will be made to a first embodiment illustrated in FIGS. 2through 7, to a second embodiment illustrated in FIGS. 8 and 9, and athird embodiment illustrated in FIGS. 10 and 11.

Surge Chamber, Baffle, Acoustic Filter, and Deflector Aspects of theNoise Suppressing Apparatus The first embodiment of muffler 2 shown inFIGS. 2 through 7 comprises a conduit means 3 which is operable totransmit exhaust fluid from the cylinder means 105.

As is shown generally in FIGS. 1, 3 and 4, conduit means 3 may bedisposed in direct metal-to-metal engagement with an exterior mountingboss 109 of the cylinder 105 and communicate directly with a cylinderexhaust port 110. This metal-to-metal juncture 111 may be supplementedby a gasket 111a as shown in FIGS. 3 and 4, but the metallic extremityof the conduit 3 is disposed largely in direct, contiguous, abuttingengagement with the metallic cylinder boss 109. Conduit means 3 may havea generally rectangular cross section extending in a directionperpendicular of longitudinal axis 301 of conduit means 3, as depictedgenerally in FIG. 4.

This longitudinal axis 301 may extend generally parallel to the axis ofcrankshaft rotation 108, when the muffler 2 is installed as shown inFIG. 1.

As shown in FIG. 4, conduit means 3 may comprise a generally tubularmetallic wall portion 302, having a generally rectangular (but roundcornered, i.e., ended) cross section extending transversely of axis 301.Conduit 3 may be somewhat composite in nature, comprising a sheet metalportion 303 connected (as by brazing) with an apertured, plate-liketerminus 304. The terminus 304, being plate-like and flat inconfiguration, will ensure contiguous, uniform and generally flushengagement between the end of the conduit 3 and the boss 109 at thejuncture zone 111.

In certain instances, conduit means 3 may not be elongate as shown inFIGS. 2 through 6, but instead may merely comprise a port or passagemeans in the base of a surge or expansion chamber 4. Such an arrangementcould result by fabricating the cylinder .mounting bosses 109 and 112,shown in FIG. 4, so that they were generally coplanar and engageablewith spaced portions of a flat boss of a muffler unit.

As noted, muffler 2 additionally includes a surge chamber 4. This surgechamber, as shown in FIG. 4, is operable to receive exhaust fluid fromthe conduit means 3 at a juncture or exhaust passage zone 401 betweenthese components.

The surge chamber 4 may be fabricated from metallic halves 402 and 403which may be telecoped together and brazed or crimped at juncture zone404.

Body or shell portion 403 of the surge chamber means may be providedwith a mounting pad zone 405 which may be disposed in direct,metal-to-metal engagement with the aforesaid mounting boss 112 which isformed on the exterior of cylinder 105. In this manner, the surgechamber means 4 is supported directly on the exterior of the cylindermeans 105.

As will be also understood from reference to FIG. 4, the conduit means 3extends between the interior of the surge chamber means 4 to thejuncture zone 111.

The surge chamber 4 may have an overall, generally rectangularconfiguration (albeit somewhat rounded) encircling the surge chamberinterior 406 (within which exhaust gas expands) and includes a generallyrectangular cross section extending generally parallel with theaforesaid principal vibration plane.

Muffler 2 further includes acoustic filter means 5 depicted generally inFIGS. 3, 4 and 5.

Acoustic filter means 5 comprises a first, generally perforate, sheetmetal cylinder means 501 having a longitudinal axis extending generallyparallel to the axis of crankshaft rotation 108. A longitudinal centralaxis 502 of the first cylinder means 501 is transversely displaced fromthe longitudinal central axis 301 of the conduit means 3. Thus, theperforate cylinder means 501 and the conduit means 3 may be consideredas being mutually transversely offset along a plane extending parallelto the aforesaid principal vibration plane.

Acoustic filter means 5 may be considered to include a second cylindermeans 503 which is contained within the first cylinder means 501. Thissecond cylinder means 503 is somewhat smaller in diameter than theinternal size of cylinder means 501 so as to be generally radiallyspaced inwardly thereof.

A cap-like, end wall or barrier 504 serves to close first end portion505 of cylinder means 501. As shown in FIG. 5, this metallic barrier cap504 may be partially telescoped within a first inner end 505 of cylinder501 and be brazed into a fixed position relative to, and connected with,cylinder 501.

Thus, cap 504 comprises a barrier means which operates to close thefirst end portion 505 of the cylinder means 501. As will be furtherrecognized, this first cylinder end portion 505 may be viewed as beinggenerally mutually contiguous with the rim of cap 504 and housed withinthe interior of 406 of the surge chamber 7 means 4.

The second or outer end 508 of cylinder 501 may be deflected generallyradially outwardly so as to provide a mounting ledge 508a. This ledge orrim may be abuttingly engageable with an annular mounting shoulder 407of the surge chamber means. Similarly, an outwardly deflected andgenerally radially extending shoulder 509 of the cylinder means 503 mayprovide a shoulder or annular rim disposed axially outwardly of, butengageable with, the rounded inner corner of shoulder 508a of the firstcylinder means 501.

This arrangement permits the cylinder means 501, including its closureor cap 504, to be telescoped through a surge chamber opening 408,provided by 7 shoulder 407, until shoulder 508a is disposed in abuttingengagement with shoulder 407. Either before or after this assembly takesplace, the inner cylinder 503 508a. In FIG. 5, sleeve 503 is showndisplaced to the right from this engagement position.

' V. Cylinder 503 and its annular rim wall 509 provide an open-ended,generally tubular means which is telescopingly mounted within tubularmeans 501, for cyclic flow restricting purposes, as will be hereinafterdescribed. This open-ended cylinder means provides a venting passage511a disposed within interior passage 511 of tubular means 503 andcommunicating with interior 406 of surge chamber 4 via open end 511b.

With this arrangement, the rim defining, upper end 509 of the innercylinder 503 comprises annular wall means extending generallytransversely of and between the second or outer end portions of thefirst and second cylinder means 501 and 503. In addition, the upper end509 of the cylinder 503, like the end 508 of cylinder 501, generallyencircles the outlet means 510 which is operable to continuouslytransmit exhaust fluid to the exterior of the surge chamber means.

The flow of this exhaust fluid to the interior passage 511 of thecomposite cylinder means 501-503 is facilitated by perforate side wall5010 of the cylinder means 501 and by the open end Sllb of cylinder 503.

Thus, as shown in FIGS. 3, 4 and 5, the outer cylinder 501 includes aplurality of generally radially extending, longitudinally elongate, andcircumferentially spaced first perforations 512. As shown in FIGS. 5andS, two such longitudinally displaced rows of perforations 512 may beprovided. One row 512a discharges into annular passage 514 betweencylinders 501 and 503 while another row 512b discharges directly intointerior 5116 at the innermost end of the acoustic filter.

It is contemplated that the width of each opening 512 may be on theorder of 0.125 inches, with the length of each such opening 512 being onthe order of 0.50 inches.

The radial gap between the cylinders 501 and 503 provides the aforesaid,constricted annular flow path 514 extending longitudinally of andinterposed generally radially between the first and second cylindermeans'50l and 503. This flow path, along with the perforation512, isbelieved to perform a significant sound attenuating function.

The constricted annular flow path 514 extends generally along the axis502. In this connection, it will be rethe aforsaid principal vibrationplane and the engine 103 are operable to generate vibrations generallyaligned with this principal vibration plane and acting on the first andsecond cylinder means 501-503. These vibrations are generated so as tobe directed generally transversely of the constricted annular flow path514 and in general alignment with the cutting plane.

Before discussing additional elements of the muffler 2, it is worthnoting that the flow of exhaust fluid between surge chamber interior 406and acoustic filter interior 511 may be somewhat multidirectional incharacter.

Some of this fluid may flow generally radially between interior space406 and space 511, while some 8 fluid flow will be resisted by the solidwall portions of side wall means 503a of cylinder 503 so as to flowgenerally longitudinally of axis 502 along the path 514, both towardarea 511(- and a flow restricting passage means 51 1d at the outer endof the acoustic filter which wiill be hereinafter described in greaterdetail.

Muffler 2 additionally may include a plurality of generally tubularcomponents 6 which function as housings for fastening members. Thesecomponents 6 may provide a form of internal baffle action in the surgechamber 4. These tubular components 6 also serve the function ofreducing the unsupported or unbraced wall or panel area of the mufflerchamber 4 and may act to reduce airborne noise eminating from vibratingwall or panel areas.

Thus, as shown in FIGS. 2 through 5, muffler 2 may include threegenerally tubular housing or baffle members 601, 602 and 603.

Each such baffle member extends generally parallel to the axis ofcrankshaft rotation and thus parallel to the axes 502 and 301.

As shown in FIGS. 2 and 3, the tubular housing or baffle members 601-603may be brazed to surge chamber shell portion 402 at a juncture 604 andextend through the surge chamber interior 406.

Two of the baffles 601 and 602 may pass longitudinally through upper andlower ends of the conduit means 3, as generally shown in FIG. 3.

The inner ends of these baffle or housing members I 601-603, i.e., theends disposed adjacent the cylinder 105, may be secured by a brazingarrangement involvcalled that axis 502 extends generally perpendicularto.

ing a telescoping assembly of components, as generally shown in FIGS. 3and 4.

Thus, as shown in FIGS. 3 and 4, a representative tubular member 602telescopingly receives a generally tubular and radially flanged fitting605. Another end of fitting 605 passes through an apertured portion ofend wall lip 305 of conduit means 3 so as to be telescopingly receivedwithin an aperture 306 of mounting plate 304. With these componentstelescopingly assembled in this manner, as shown generally in FIGS. 3and 4, the brazing of a fitting 605 to an end of tubular member 602 andto the base plate 304 will serve to effectively interconnect thecomponents 602, 303 and 304.

The arrangement described in connection with member 602 is duplicatedwith respect to member 60].

This same general mode of assembly may be employed in connection withtubular member 603. This member may be secured by brazing to mountingpad portion 405 of shell 403. In this case, opposite ends of a tubularflanged fitment 606 may be partially telescopingly received within anend of tubular member 603 and an opening wall 405, respectively, and bebrazed to these components so as to effect their interconnection.

With respect to the general orientation of components heretoforedescribed, it is of significance to note that the conduit means 3, thefirst and second cylinder means 501 and 503, the constricted annularflow path 514, and the tubular baffle means 601603 are all arranged sothat their longitudinal axes are generally mutually parallel. All ofthese components are subject to vibrations generated in generalalignment with the principal vibration plane heretofore described.

The precise baffle phenomenon which may be attributable to the bafflemeans 601-603 is not fully understood. Nevertheless, it is believed thatthe nonsymmetric disposition of these baffle means, spaced generallyradially outwardly of the cylinder means 501, contribexiting from outletmeans 510 in a direction extending generally transversely of the axis ofcrankshaft rotation,

albeit displaced from this axis.

Thus, deflector means 7 may include arcuate wall 1 means 701 having agenerally quarter-sphereconfiguration.

This quarter-sphere configuration is oriented such that its center ofcurvature 702 is generally coincident with the centrallongitudinal axis502 common to the first and second cylinder means 501 and 503,respectively. I

The manner in-which the deflector means 7 is installed will beappreciated by reference to FIGS. 2 through 5.

Thus, as there shown, quarter-sphere wall 701 may be supported on amounting rim 703 which has apertured clampor ear means 704 and 705.

With the cylinder assemblies 501 and 503 positioned as shown in FIG. 5,the rim 703 may be positioned so as to dispose the apertured earportions 704 and 705 in general alignment with threaded fastenerreceiving openings 710 and 711 formed on surge chamber means 4. Theinsertion of threaded fasteners 712 and.713 through these ear portionsand fastener receiving openings into threaded cooperation with threadednut means 714 and .715 (brazed to the. interior of surge chamber 4) willcomplete the installation of the deflector assembly.

This completion of the deflector installation will concurrently serve tosecure the cylinder means 501 in position and limit the telescopingmovement of cylinder 503, as hereinafter described. This will result, asshown in FIG. 5, due to a generally abuttable engagement between the rim703 and the cylinder flange 508a, and to deflector 701 providing a stop701a to limit outer telescoping movement of cylinder503 relative'tocylinder 501 and, passage 511d. In this assembled position, opening 707of rim 703 will be, coaxially aligned with, the generally coextensivewith, outlet 510.

The position f the threaded fasteners 712 and 713 and their associatedthreaded nut means 714 and 715 may besuch, as shown generally-in FIGS. 2and '5, as to cause the deflector wall 701 to be disposed with itsopening 716 directed directly downwardly, i.e., away from the upper partof the chain saw where an operators hands would be disposed.

In certain instances, the deflector may be inverted and the wall means701 configured so as to provide a deflected flow of exhaust fluid ontoan operators hands for operator hand warming purposes.

The deflector 701 may also be oriented so as to deflect warm exhaustfluid into portions of the chain saw for the purpose of warmingcomponents such as' the carburetor, air filter, etc. located generallyin upper area 113 of the chain saw-,shown in FIG. 1.

While the general manner-in which the muffler 2 is mounting screws 609which pass through the fitments 605 and 606 into cylinder bosses 109 and112, respectively. Y

The muffler 2, as heretofore described, will function to effectivelyattenuate noise generated by the engine means 103 through thesynergistically cooperating interaction of the exhaust passage means 3,surge chambermeans 4, acoustic filter means 5, and cyclically operableflow restricting means 503 and 509, possibly fa cilitated by baffleaction provided by baffle means 6.

Exhaust fluid will flow from the cylinder discharge port 1 10 into thesurge chamber interior 406 by way of exhaust passage 3 and expandtherein. Baffling of this flow will result if the conduit means 3 andthe cylinder means 501 and 503 are displaced. Further baffling of thisflow may result from a nonsymmetric orientation and presence of thebaffle means 601-603.

A thus baffled flow of fluid in the surge chamber 4 will pass throughthe perforation means 512 for acoustic filtering, i.e., noiseattenuation, and thereafter be transmitted to the exhaust outlet 510.

Cyclically Operable Flow Restriction Subsequent to the initiation ofacoustic filtering of the exhaust flow, a unique modification involvingan advantageous blunting of pressure pulses, or dissipating or spreadingof noise energy so as to reduce peak noise intensity, may be achieved bycyclically restricting the outflow of exhaust gas from the acousticfilter 5 while providing for continuous unimpeded venting of a portionof exhaust flow from the acoustic filter.

One manner in which cyclic restriction and continuous venting may beachieved is described in the aforesaid parent application Ser. No.220,632 with reference to FIGS. 11 through 13. Accordingly, thedisclosure of the aforesaid parent application Ser. No. 220,632 as itrelates to this technique (i.e., the embodiment of FIGS. 11 through 13of the parent application) is herein incorporated by reference. However,the present invention, while entailing certain generic aspects of thenoise attenuating function of the continuously venting, cantilever reedarrangement featured in FIGS. 11 through 13 of the aforesaid parentapplication (which provides cyclic restriction and concurrent continuousventing of the exhaust flow issuing from an acoustic filter), materiallyand nonobviously departs from the species teaching of this parentapplication and provides a unique new species for achieving cyclicrestriction and concurrent continuous venting;

Distinctive characteristics of this new concept reside in part in theutilization of a freely movable or unbiased, cyclically operable, flowrestricting mechanism.

This new concept will now be described with reference to FIGS. 2, 5, and6 through 11 of the present application.

Unimpeded, Cyclically Operable Flow Restriction and ConcurrentContinuous venting 2. the perforate flow baffling, and acousticfiltering cylinder-like wall 501,

3. the annular passage 514 including the outlet, flowcontrolling,annular passage portion 511d,

4. the inner portion of the deflector 701 which cooperates with the rim5080 to define stop means which determine the extremities of telescopingmovement of the cylinder 503 relative to the annular passage 514 and thecylinder 501, and

5. continuous venting passage means 510-51 la-51 1c which communicatedirectly with openings 512b of the acoustic filter 5.

As will be apparent by reference to FIG. 5, where the assembled muffler2 is shown, when the sleeve 503 is disposed in the innermost telescopedposition, the sleeve flange 509 extends transversely across the annularpassage means 511d so as to effectively restrict and substantially closeoff this portion of the exhaust gas flow path.

When the sleeve 503 telescopes to the left as shown in FIG. 5, theflange 509 moves away from the annular passage 511d so as to reduce flowrestriction with respect to exhaust gas flowing to the left throughannular passage 514 and to the atmosphere via cyclically restricted,annular passage 511d.

It is believed that impacting engagement between flange 509 and theinterior 701a of deflector portion 701 will induce a rebounding orrestitution effect, tending to cause the sleeve 503 to rebound backtoward the right from the position shown in FIG. 5 so as to induce theincrease in restriction of passage means 511d (by causing the flange 509to progressively move into sub stantially closing cooperation with thepassage portion 51 1d). 1

At this juncture, it is significant to note that the sleeve 503 ismounted for free telescoping movement and is not biased toward anyparticular extremity of its range of telescoping movement. Moreover, thesleeve 503 is free, to some extent and while at rest, to cant" withinthe outer sleeve 501.

Observations to dateindicate that the telescoping movement of sleeve-503may-be related to the pressure pulses of the exhaust gas so as to besomewhat out of phase i.e., be delayed in opening movement relative topressure pulse peaks.

In short, instead of the sleeve 503 moving away from the passage 511d aswould be expected, surprisingly and unexpectedly the sleeve 503 and itsflange 509 is believed to undergo movement to the right, from theposition shown in FIG. 5, during positive pressure pulses.

Whatever the explanation may be, a heretofore unexpected reduction inthe noise level of chain saws is produced which is particularlyeffective in the median and low speed range of chain saw operation inthat a significant noise level reduction is accomplished whilemaintaining adequate engine power.

Moreover, these desirable objectives are achieved without generatingannoying rattling noise as a result of the oscillating or telescopingaction of the sleeve 503. It may well be that the significant absence ofexcessive rattling noise is a result of a form of air cushioningresulting from the cyclic movements of the sleeve 503 being in asomewhat out-of-phase relation with the pressure pulses of the exhaustgas, i.e., with the flange 509 tending to seat on the rim 508 duringportions of positive pressure pulses.

12 Having now described in detail and in relation to one preferredembodiment what are believed to be significant structural and operatingcharacteristics of the cyclic flowing restricting and venting mechanism8, it is now appropriate to summarize the overall mode of operation ofthe muffler or noise reducing apparatus 2.

SUMMARY OF MODE OF OPERATION In summarizing the mode of operation ofmuffler 2, reference will be made to FIGS. 2 through 7 as well as toFIG. 12.

FIG. 12 schematically illustrates, in a functional sense, various noisereducing or attenuating functions which are performed by the totality ofoperations of the preferred embodiment. However, as will be apparent vby definitional aspects of the appended claims, at least some advantagesof the invention may be attained by implementing only certain of thefunctions depictedby FIG. 12.

The overall improvement in the noise reducing apparatus 2 resides in anapparatus as follows.

An exhaust passage means 3 communicates with the working chamber means105 of the chain saw engine means 103 and is operable to transmit a flowof cyclically pulsing exhaust gas therefrom. The surge chamber means 4is operable to receive the flow of exhaust gas from the exhaust passagemeans 3 and transmit it to acoustic filter means 5.

The acoustic filter means 5 includes generally tubular means 501including lateral wall means defining interior passage means 511communicating with the atmosphere and extending within the surge chambermeans 4. Acoustic filter means 5 further includes transverse passagemeans 512 intersecting the lateral wall means of the generally tubularmeans 501 and providing restricted, acoustic filtering, fluidcommunication between'the surge chamber means 4 and the interior passagemeans 511 of the generally tubular means 501.

A flow restricting means 8 is mounted in'the generally tubular means 501and is operable to cyclically restrict at least a portion'of the flow ofexhaust gas. A continuously operable venting means 511a-510 is operablyassociated with the generally tubular means 501 and is operable tomaintain a continuously open flow path 511a-510 between the surgechamber'means 4 and the atmosphere, through which path at least aportion of the flow of exhaust gas from the chain saw engine means 103may continuously pass.

The noise reducing apparatus 2 may include a plurality of asymmetricallyarranged tubular members 601, 602, 603 defining baffle means 6 containedwithin the surge chamber means 4 and operable to baffle the flow ofexhaust gas within the surge chamber means 4 between the exhaust passagemeans 3 and the acoustic filter means 5.

The flow restricting means 8 is free floating and telescopinglyassociated with the tubular means 501 and is supported by the noisereducing apparatus 2 for substantially unimpeded reciprocating movementrelative to the tubular means 501. This flow restricting means 8includes wall means(i.e., 503a or 503a or 503a) telescopingly receivedwith the tubular means 501 and operable to cooperate with the lateralwall means of the tubular me ans interior passage means 5 ll of thetubular means and define generally annular passage means 514 within theinterior passage means 51 1. The annular passage means 514 is operableto deflect a flow of exhaust gas passing transversely of the lateralwall means through the transverse passage means 512 and cause thisdeflected flow of exhaust gas to flow generally longitudinally of theinterior passage means 511 The continuously operable venting means511a-510 comprises a generally central, venting passage means 511aextending generally centrally and longitudinally of each of the flowrestricting means 8 and the annular passage means 514, with this ventingpassage means being defined by and carried by the flow restricting means8.

The generally annular passage means 514 provides fluid communicationbetween the generally central,

venting passage means 511a and the interior 406 of surge chamber means4. The generally annular passage means 514 is also operable to providefluid communication, independent of the generally central ventingpassage means 511a, between the atmosphere and said surge chamber meansinterior 406 via outlet 511d.

The flow restricting means 8 includes generally annular, flowrestricting wall means 509 extending transversely of the generallyannular passage means 514. The wall means 509 is cyclically operable inresponse to the flow of exhaust gas to cyclically restrict a portion511d of the annular passage means 514 communicating with the atmosphere.The generally annular wall means 509 is operable to move away from theannular passage means 514 and tend to reduce restriction of thegenerally annular passage means area 511d and is operable to move towardthe annular passage means portion 511d and increase restriction of thegenerally annular passage means 514.

The noise reducing apparatus 2 may further include flow deflecting means7 providing exhaust gas deflecting, fluid communication between the flowof exhaust gas issuing from the interior passage means 51 1 and theatmosphere. This flow deflecting means 7 includes restitution means 701aoperable 1) to be impacted by the flow restricting means 8, when thegenerally annular wall means 509 is moving away from the annular passagemeans 514 and tending to reduce the restriction of the generally annularpassage means 514 and 2) to induce a rebounding of the flow restrictingmeans 8 tending to move the generally annular wall means 509 toward theannular passage meand 514 and induce an increase in restricting of thegenerally annular passage means 514.

The transverse passage means 512 of the acoustic filter means mayinclude a first plurality 512a of elongate openings extendinglongitudinally of the generally annular passage means 514, spacedcircumferentially about the generally tubular means 501, and operable todischarge exhaust gas directly into the generally annular passage means514. The transverse passage means 512 may further include a secondplurality 51219 of elongate openings, comprising, in effect, a portionof the continuously operable venting means, and operable to dischargeexhaust gas into the interior passage means 511C without passage throughthe generally annular passage means 514.

In summary, then, and by reference to FIG. 12, it will be appreciatedthat the following sound attenuating functions are performed by thetotality of components included in muffler 2:

Exhaust gas is received by inlet passage means 3, as depicted infunction block A of FIG. 12;

Exhaust gas is expanded within surge chamber 4, as depicted in block Bof FIG. 12;

Exhaust gas is baffled by baffle means 6 and/or perforation means 512,as depicted by block C in FIG. 12;

Exhaust gas is acoustically filtered so as to attenuate noise levels byacoustic filter means 5, as depicted by block B of FIG. 12;

Exhaust gas is cyclically restricted and is continuously vented (asimplemented by flow restricting and venting means 8), as generallydepicted in block E of FIG. 12;

Exhaust gas is deflected by deflecting means 7 as it issues from theacoustic filter means 5 under the control of flow restricting andventing means, 8 as generally depicted by block F of FIG. 12; and

Noise modulated exhaust gas is discharged to the atmosphere as generallydepicted by block G of FIG. 12.

ALTERNATIVE FORMS OF APPARATUS As will be recognized from the priordiscussions, the invention may be practiced in a variety of structuraland operational formats, consistent with disclosures of either or bothof the present application and the aforesaid parent application Ser. No.220,632. However, particularly significant results are attributed to theunbiased flow restricting action of the cyclic restricting and ventingmeans 8 of the present invention.

For example, the dimensions and configurations and overall arrangementof interior passage means 3 and surge chamber 4 may be substantiallyvaried, as may be the dimensions, arrangement, shapes and numbers of thebaffle means 6 (i.e., 601, 602, 603) and/or passages 512.

Moreover, the deflector 7 may be significantly altered in form, size andshape as may be the acoustic filter 5.

Furthermore, the invention may be practiced without all of thecomponents identified in FIG. 12 being necessarily present.

With respect to the phase restricting and venting means 8, a variety ofstructural modifications are foreseeable which would serve to vary thestructural nature of the cylinder or floating thimble or valve" 503, theradial width of the gap 514, the size of the vent opening 510, and theweight and length of the mechanism 8.

For example, as shown in FIGS. 8 and 9, mechanism 8 may comprise amodified cylinder 503 having a perforate sidewall 503a and annular rim509 which provides an orifice-like, central opening 510 and a somewhatnarrower width for passage 514. Wall 5030 may be provided with a seriesof circumstantially spaced longitudinally elongate ports or openings503b.

A still further modification of mechanism 8 is dis closed in FIGS. 10and 11.

As they are shown, a cylinder-like component 503 is provided with sidewall means 503a" defined by a plurality of circumferentially spaced,leg-like components 503C. The legs 503c are connected with a platelikerim defining component 509" which affords a central, orifice-like ventoutlet 510".

With respect to the three embodiments of mechanism 8 heretoforedescribed, it is believed that a variety of other configurations may befeasible along with these embodiments, but at the present time, theFIGS. 6 and 7 species is believed to be particularly effective,structurally simple, and operationally reliable.

In connection with all of the species heretofore described, it iscontemplated that the length of the cylinder side wall (i.e., the sidewall 503a of the FIGS. 6 and 7 species, for example) would be such asshown in FIG.

- 5 as to substantially overlap the outermost row of perforded byperforation means 512a will be cylically reduced as a result of theouter telescoping of the cylinder 503 (i.e., due to uncovering ofperforation means 51211).

All this notwithstanding, it is believed that the invention might alsobe able to be effectively practiced with the length of the sleeve sidewall (such as, for example, wall 503a) being extended so as to overlapin whole or in part the perforation means 51212 or extend generallydeeper or further into'the cylinder 501.

' It is also contemplated that the wall structure of the acoustic filter5 may vary, particularly in accordance with the prior teaching of ourparent application Ser. No. 220,632.

Thus. for example, the mechanism 8 of the present invention may betelescopingly mounted within a single cylinder 501 as shown in theaforesaid parent application or may be telescopingly mounted within adoublewalled acoustic filtering, cylinder arrangement depicted in FIG. 8of the aforesaid parent application (i.e., telescopingly mounting withina perforated metal inner wall component 503 illustrated in FIG. 8 of theaforesaid parent application). This arrangement would produce a pair ofcoaxially arranged acoustic filtering,

annular passages, one existing between the cylinder walls 501 and 503 ofthe aforesaid parent application and the other existing between thecylinder 503 of the aforesaid parent application and the side wall 503of the mechanism 8 of the present invention (i.e., for example, 503a).

Moreover, it is contemplated that as a single cylinder 501 is employed,a uniform pattern of relatively small perforations could be employed, inlieu of the elongate slot featured in the present disclosure, along withother transverse opening arrangements. Such a uniform patternarrangement is described, for example, in the aforesaid parentapplication in relation to inner sleeve or cylinder 503 of thatapplication.

SUMMARY OF MAJOR ADVANTAGES AND SCOPE OF INVENTION A particularadvantage of the invention resides in the manner in which effectivenoise reduction and attenuation is achieved without sacrificingexcessive engine power, particularly at low and median speeds of engineoperation. In the present invention, a noise level reduction on theorder of five or so decibels has been attained.

The free floating (i.e., unimpeded or unbiased) aspects of mechanism 8eliminate the necessity of employing biasing means and are believed tocontribute to the attainment of the aforesaid phase control aspects ofthe invention.

A minimization or suppression of rattling of the control mechanism 8 isattained which is believed to be particularly desirable. This may beattributed, in part, to air cushioning which could result from themechanism 8 cycling in a somewhat out-of-phase relation with positivepressure peaks of the exhaust gas.

Somewhat surprisingly, the oscillation of mechanism 8 occurs in theabsence of a biasing or restoring mecha- 16 nism even with thismechanism being free to cant or incline within the acoustic filter. Thisfeature alone attests to the unobviousness of the invention andconstitutes an independently significant aspect of the invention.

Indications of the wide range of variations, of both a structural andfunctional sense, within which the invention may be practiced haveheretofore been indicated. As will also be appreciated, the unique noisereducing aspects of the invention are believed applicable to operatingcontexts other than those associated with chain saws, even-though thechain saw environment is believed to constitute a particularlysignificant application of the invention. However, noise reducingaspects of the invention may be applied to other environments such as,for example, internal combustion engineoperated small generators wherenoise reduction of small engines is a highly desirable feature.

Bearing these criteria in mind, it will be recognized that those skilledin the art and familiar with the present disclosure and the disclosureof the aforesaid parent application may envision additions, deletions,substitutions, modifications or arrangements equivalent in whole or inpart to the invention as heretofore described, but which would fallwithin the purview of the invention as set forth in the appended claims.

What is claimed is:

1. In a chain saw including an apparatus for reducing the noisegenerated by chain saw operation, and

, wherein said chain saw includes chain saw cutting means includingguide bar means, and cutter chain means supported on said guide barmeans for traversal through a cutting path; and chain saw power meansincluding chain saw engine means having a working chamber means, andchain saw power transmitting means operable to transmit driving force tosaid cutter chain means and cause said cutter chain means to traversesaid cutting path; the improvement in said noise reducing apparatuscomprising: exhaust passage means communicating with said workingchamber means of said chain saw engine means and operable to transmit aflow of cyclically pulsing exhaust gas therefrom; generally tubular,outlet passage means operable to receive said flow of exhaust gas andtransmit said flow to the atmosphere; exhaust flow responsive,cyclically operable flow restricting means telescopingly mounted in saidoutlet passage means and operable in response to pressure pulsations insaid flow of exhaust gas to cyclically restrict a portion of said flowof exhaust gas transmitted through said outlet passage means;continuously operable venting means operable to permit a continuous flowof a portion of said flow of exhaust gas through said outlet passagemeans to the atmosphere concurrent with said cyclic restriction of aportion of said exhaust flow through said outlet passage means; and 2.In a chain saw including an apparatus for reducing the noise generatedby chain saw operation, and wherein said chain saw includes chain sawcutting means including guide bar means, and

chain saw power means including chain saw engine means having a workingchamber 18 means being defined by and carried by said flow restrictingmeans; said generally annular passage means providing fluidcommunication between said generally cenmeans, and tral, venting passagemeans and said surge chamchain saw power transmitting means operable tobet means;

transmit driving force to said cutter chain means Said generally annularpassage means being operaand cause said cutter chain means to traverseble to Provide fluid Communication, independent said cutting path; ofsaid generally central venting passage means, improvement in said noisereducing apparatus combetween Said atmosphere and Said Surge chamberprising: means; exhaust passage means communicating with said said flowrestricting means including generally working chamber means of saidchain saw engine nular, flow restrifiting Wan means extendmg means andoperable to transmit a flow of cyclitransversely of Sald generallyannular Passage ll l i exhaust gas therefrom; means and cyclicallyoperable in response to said surge chamber means operable to receivesaid flow flow 9 exhaust gas to cyclically restrict a P n of exhaust gasfrom said exhaust passage means; annular mefms Commumcatmg acoustic filtmeans including with said atmosphere, with said generally annulargenerally tubular means including lateral wall means bemg operable tomove away from means defining interior passage means commu said annularpassage means and tend to reduce .nicating with the atmosphere andextending restnct1on of said generally annular passage within SaidSurge. chamber means, and I means and operable to move toward saidannular transverse passage means intersecting said lateral passage meansand Increase restncnon of Sald wall means of said generally tubularmeans and f f y?" passage i h l providing restricted, acousticfiltering, fluid h a m apparati; me u communication between said surgechamber e ecimg means P mg ex dust gas 8' means and the interior passagemeans of said flectmg cpminumcatlon i p Said flow generally tubularmeans; of exhaust gas issuing from said interior passage flowrestricting means mounted in said generally $222: atmosphere Sald flowdeflectmg tubular means and operable to cyclically restrict grestriction means operable to be impacted by at least a portion of saidnew of exhaust said flow restrictin means when said enercontinuouslyoperable venting means operably asg ally annular wall means [8 movingaway from soclated wlth $2.1m generally .tubular means and said annularpassage means and tending to re- 1 operable to mamtam a continuouslyopen flow duce the restriction of said generally annular path betweensaid surge chamber means and said passage means and induce a reboundingof atmosphere through which lelast a Portion of said flow restrictingmeans tending to move P flow of exhaust g from Sald cham Saw saidgenerally annular wall means toward said gme means may continuouslypass; annular passage means and induce an increase said noise reduc ngapparatus including a plurality 40 in restricting of Said generallyannular passage of assymetrically arranged tubular members demeans;finmg baffle means comamed with! Surge said transverse passage means ofsaid acoustic filter chamber means and operable to baffle said flowmeans including of exhaust gas within said surge chamber means a firstplurality of elongate openings extending betweefl 531d exhaust Passagemeans and 531d longitudinally of said generally annular passage acousticfine]- means; v means, spaced circumferentially about said said flowrestricting means being telescopingly asgenerally tubular means andoperable to Sociated with said tubular means and Supported chargeexhaust gas directly into said generally by said noise reducingapparatus for substantially annmar passage means and unimpededreciprocating movement relative to a Second plurality of elongateopenings comp i Said la means; ing a portion of said continuouslyoperable said flow restricting means including wall means venting meansd bl to di h telescoping)? received with s tubular means haust gas intosaid interior passage means withand operable to cooperate lateral W3."out passage through generally annular pasmeans and interior passagemeans of said tubular sage means means and define generallyannularpassage means within said interior passage means operable to deflect aflow of exhaust gas passing transversely of said lateral wall meansthrough said transverse pas- 0 sage means and cause said deflected flowof exhaust gas to flow generally longitudinally of said interior passagemeans;

3. In a chain saw including an apparatus for reducing the noisegenerated by an operating chain saw, wherein said chain saw includeschain saw cutting means including guide bar means, cutter chain meanssupported on said guide bar means for movement through a cutting plane;chain saw engine means including said continuously operable ventingmeans comprising generally central venting passage means extendinggenerally centrally and longitudinally of each of said flow restrictingmeans and said annular passage means, with said venting passage pistonsaid cylinder means,

crankshaft means driven by said piston means of said piston and cylindermeans, and operable to transmit driving force to said cutter chainmeans;

said noise reducing apparatus comprising:

19 conduit means operable to transmit cyclically pulsing exhaust fluidfrom said cylinder means of said piston and cylinder means; I surgechamber means,

said surge chamber means being operable to receive exhaust fluid fromsaid conduit means; acoustic filter means including generally perforate,outlet passage defining means, said conduit means and said outletpassage defining means being mutually offset,

barrier means within said surge chamber means closing a first endportion of said outlet passage defining means.

outlet means provided by a second end of said outlet passage definingmeans,

said outlet means being operable to transmit exhaust fluid to theexterior of said surge chamber means,

said outlet passage defining means including a plurality of openingsproviding communication between said outlet means and the interior ofsaid surge chamber means;

a plurality of tubular baffle means,

said tubular baffle means being located within the interior of saidsurge chamber means,

said tubular baffle means being mutually displaced and disposednonsymmetrically in relation to said outlet passage defining means; and

flow restricting means operable to cyclically restrict a flow of saidexhaust fluid passing through said acoustic filter means; a

continuously operable venting means operable to permit a continuous flowof at least a portion of a flow of said exhaust fluid through saidacoustic filter means to the atmosphere; and support means mounting saidflow restricting means for substantially unimpeded cyclic movement.

4, In a chain saw including an apparatus for reducing the noisegenerated by an operating chain saw, wherein said chain saw includeschain sawcutting means includin guide bar means,

cutter chain means supported on said guide bar means for movementthrough a cutting plane with said cutting plane being aligned ingenerally parallel relation with a principal vibration plane of a chainsaw;

chain saw engine means including piston and cylinder means,

crankshaft means driven by said piston means of said piston and cylindermeans, and operable to transmit driving force to said cutter chainmeans;

and said crankshaft means being mounted for rotation about an axis ofcrankshaft rotation extending generally perpendicular to said principalvibration plane; said noise reducing apparatus comprising:

conduit means operable to transmit cyclically pulsing exhaust fluid fromsaid cylinder means of said piston and cylinder means,

said conduit means having a longitudinal axis extending generallyparallel to said axis of crankshaft rotation;

surge chamber means,

said surge chamber means being operable to receive exhaust fluid fromsaid conduit means,

said surge chamber means having a generally rectangular cross sectionextending generally parallel with said principal vibration-planejacoustic filter means including a generally perforate cylinder meanshaving a longitudinal axis extending generally parallel to said axis ofcrankshaft rotation,

a longitudinal, generally central axis of said cylinder means beingtransversely displaced from a longitudinal, generally central axis ofsaid conduit means, with said conduit means and said cylinder meansbeing mutually, transversely offset,

barrier means within said surge chamber means closing a first endportion of said cylinder means,

outlet means provided by a second end of said cylinder means, I Y

said outletmeans being operable to transmit exhaust fluid to theexterior of said surge chamber means,

said cylinder means including a plurality of generally radially openingand circumferentially spaced perforation means,-

said cutter chain means and chain saw engine means being operable togenerate vibrations generally aligned with said principal vibrationplane and acting on said cylinder means to generate vibrations thereindirected generally transversely thereof and in general alignment withsaid principal vibration plane;

' flow restricting means operable to cyclically restrict a flow of saidexhaust fluid passing through said acoustic filter means;

continuously operable venting means operable to permit a continuous flowof at least a portion of a flow of said exhaust fluid through saidacoustic filter means to the atmosphere; and

support means mounting said flow restricting means for substantiallyunimpeded cyclic movement.

5. In a chain saw including an apparatus for reducing the noisegenerated by an operatingchain saw, wherein said chain saw includes Ichain saw cutting means including guide bar means, i cutter chain meanssupported on said guide bar means for movement through a cutting plane,with said cutting plane being aligned in generally parallel relationwith a principal vibration plane of a chain saw; 1 i chain saw enginemeans including piston and cylinder means, crankshaft means driven bysaid piston means 'of said piston and cylinder means, andgoperable totransmit driving force to said cutter chain means, said'crankshaft meansbeing mounted for rotation about an axis of crankshaft'rotationextending generally perpendicular to said principal vibration plane;said noise reducing apparatus comprising:

conduit means operable to transmit cyclically pulsing exhaust fluid fromsaid cylinder means of said piston and cylinder means, said conduitmeans having a generally rectangularlyelongate cross section, and

said conduit means having a longitudinal axis extending generallyparallel to said axis of crankshaft rotation; surge chamber means,-

said surge chamber means being operable to receive exhaust fluid fromsaid conduit means,

said surge chamber means being supported on the exterior of saidcylinder means,

said conduit means extending from said surge chamber means and beingdirectly connected with the exterior of said cylinder means and disposedin direct, metal-to-metal engagement therewith,

said surge chamber means having a generally rectangular configurationincluding a generally rectangular cross section extending generallyparallel with said principal vibration plane;

acoustic filter means including generally perforate cylinder meanshaving a longitudinal axis extending generally parallel to said axis ofcrankshaft rotation,

a longitudinal, generally central axis of said cylinder means beingtransversely displaced from a longitudinal, generally central axis ofsaid conduit means, with said conduit means and said cylinder meansbeing mutually, transversely offset,

barrier means within said surge chamber means.

closing a first end portion of said cylinder means, outlet meansprovided by a second end of said second cylinder means, said outletmeans being operable to transmit exhaust fluid to the exterior of saidsurge chamber means, said cylinder means including a plurality ofgenerally radially opening and circumferentially spaced perforationmeans, and said cutter chain means and chain saw engine means beingoperable to generate vibrations generally aligned with said principalvibration plane and acting on said cylinder means to generate vibrationstherein directed generally transversely thereof and in general alignmentwith said principal vibration plane; a plurality of tubular bafflemeans,

said tubular baffle means being located within the interior of saidsurge chamber means, each said tubular baffle means extending generallyparallel to said axis of crankshaft rotation, and said tubular bafflemeans being mutually displaced and spaced generally radially outwardlyof said cylinder means; said conduit means, said cylinder means, andsaid tubular baffle means being generally mutually parallel and subjectto said vibrations generated in general alignment with said principalvibration plane; flow restricting means operable to cyclically restricta flow of said exhaust fluid passing through said acoustic filter means;continuously operable venting means operable to permit a continuous flowof at least a portion of a flow of said exhaust fluid through saidacoustic filter means to the atmosphere; and support means mounting saidflow restricting means for substantially unimpeded cyclic movement. 6. Anoise reducing apparatus for a cyclic, internal combustion engine, saidapparatuscomprising:

exhaust passage means operable to communicate with a working chambermeans of cyclic, internal combustion engine means and operable totransmit a flow of cyclically pulsing exhaust gas therefrom;

22 generally tubular, outlet passage means operable to receive said flowof exhaust gas and transmit said flow to the atmosphere; exhaust flowresponsive, cyclically operable, flow restricting means telescopinglymounted in said outlet passage means and operable in response topressure pulsations in said flow of exhaust gas to cyclically restrict aportion of said flow of exhaust gas transmitted through said outletpassage means;

continuously operable venting means operable to permit a continuous flowof a portion of said flow of exhaust gas through said outlet passagemeans to the atmosphere concurrent with said cyclic restriction of aportion of said exhaust gas flow through said outlet passage means; and

support means including said outlet passage means,

telescopingly mounting said flow restricting means for substantiallyunimpeded cyclic movement.

7. In a chain saw including an apparatus for reducing the noisegenerated by chain saw operation. and wherein said chain saw includeschain saw cutting means including guide bar means, and cutter chainmeans supported on said guide bar means for traversal through a cuttingpath; and chain saw power means including chain saw engine means havinga working chamber means, and chain saw power transmitting means operableto transmit driving force to said cutter chain means and cause saidcutter chain means to traverse said cutting path; the improvement insaid noise reducing apparatus comprising:

exhaust passage means communicating with said working chamber means ofsaid chain saw engine means and operable to transmit a flow ofcyclically pulsing exhaust gas therefrom;

surge chamber means operable to receive said flow of exhaust gas fromsaid exhaust passage means;

acoustic filter means including generally tubular means includinglateral wall means defining interior passage means communicating withthe atmosphere and extending within said surge chamber means, and

transverse passage means intersecting said lateral wall means of saidgenerally tubular means and providing restricted, acoustic filtering,fluid communication between said surge chamber means and the interiorpassage means of said generally tubular means;

flow restricting means mounted in said generally tubular means andoperable to cyclically restrict at least a portion of said flow ofexhaust gas; and

' continuously operable venting means operably associated with saidgenerally tubular means and operable to maintain a continuously openflow path between said surge chamber means and said atmosphere throughwhich at least a portion of said flow of exhaust gas from said chain sawengine means may continuously pass;

said flow restricting means being telescopingly associated with saidtubular means and supported by said noise reducing apparatus forsubstantially unimpeded reciprocating movement relative to said tubularmeans;

said flow restricting means including wall means telescopingly receivedwith said tubular means and op- 23 erable to cooperate with said lateralwall means and interior passage means of said tubular means and definegenerally annular passage means within said interior passage means;

said continuously operable venting means comprising generally centralventing passage means extending generally centrally and longitudinallyof each of said flow restricting means and said annular means, with saidventing passage means being defined by and carried by said flowrestricting means;

said generally annular passage means providing fluid communicationbetween said generally central, venting passage means and said surgechamber means;

said generally annular passage means being operable to provide fluidcommunication, independent of said generally central venting passagemeans, be-

tween said atmosphere and said surge chamber means; and

said flow restricting means including generally annular, flowrestricting wall means extending transversely of said generally annularpassage means and cyclically operable, in response to said flow ofexhaust gas, to cyclically restrict a portion of said annular passagemeans communicating with said atmosphere. with said generally annularwall means being operable to move away from said annular 1 passage meansand tend to reduce restriction of said generally annular passage meansand operable to move toward said annular passage means and increaserestriction of said generally annular passage means.

8. In a chain saw including an apparatus for reducing the noisegenerated by chain saw operation. and wherein said chain saw includeschain saw cutting means including guide bar means, and

cutter chain means supported on said guide bar means for traversalthrough a cutting path; and

chain saw power means including chain saw engine means having a workingchamber means, and

chain saw power transmitting means operable to transmit driving force tosaid cutter chain means and cause said cutter chain means to traversesaid cutting path;

the improvement in said noise reducing apparatus comprising: exhaustpassage means communicating with said working chamber means of saidchain saw engine means and operable to transmit a flow of cyclicallypulsing exhaust gas therefrom; surge chamber means operable to receivesaid flow of exhaust gas from said exhaust passage means. acousticfilter means including generally tubular means including lateral wallmeans defining interior passage means communicating with the atmosphereand extending within said surge chamber means, and transverse passagemeans intersecting said lateral wall means of said generally tubularmeans and providing restricted, acoustic filtering, fluid communicationbetween said surge chamber means and the interior passage means of saidgenerally tubular means;

24 flow restricting means mounted in said generally tubular means andoperable to cyclically restrict at least a portion of said flow ofexhaust gas; and continuously operable venting means operably associated with said generally tubular means and operable to maintain acontinuously open flow path between said surge chamber means and saidatmosphere through which at least a portion of said flow of exhaust gasfrom said chain saw engine means may continuously pass; said noisereducing apparatus including baffle means contained within said surgechamber means and operable to baffle said flow of exhaust gas withinsaid surge chamber means between said exhaust passage means and saidacoustic filter means; said flow restricting means being telescopinglyassociated with said tubular means and supported by said noise reducingapparatus for substantially unimpeded reciprocating movement relative tosaid tubular means; said flow restricting means including wall meanstelescopingly received with said tubular means and operable to cooperatewith said lateral wall means and interior passage means of said tubularmeans and define generally annular passage means within said interiorpassage means operable to deflect a flow of exhaust gas passingtransversely of said lateral wall means through said transverse passagemeans and cause said deflected flow of exhaust gas to flow generallylongitudinally of said interior passage means; said continuouslyoperable venting means comprising generally central venting passagemeans extending generally centrally and longitudinally of each of saidflow restricting means and said annular passage means, with said ventingpassage means being defined by and carried by said flow restrictingmeans; said generally annular passage means providing fluidcommunication between said generally central, venting passage means andsaid surge chamber means; said generally annular passage means beingoperable to provide fluid communication, independent of said generallycentral venting passage means, between said atmosphere and said surgechamber means; said flow restricting means including generally annular,flow restricting wall means extending transversely of said generallyannular passage means and cyclically operable in response to said flowof exhaust gas to cyclically restrict a portion of said annular passagemeans communicating with said atmosphere, with said generally annularwall means being operable to move away from said annular passage meansand tend to reduce restriction of said generally annular passage meansand operable to move toward said annular passage means and increaserestriction of said generally annular passage means; and said noisereducing apparatus further including flow deflecting means providingexhaust gas deflecting, fluid communication between said flow of exhaustgas issuing from said interior passage means and said atmosphere, saidflow deflecting means including 25 26 restitution means operable tobe'impacted by said flow restricting means tending to move said flowrestricting means, when said genersaid generally annular wall meanstoward said ally annular wall means is moving away from I annularpassage means and induce an increase said annular passage means andtending to re v in restricting of said generally annular passage ducethe restriction of said generally annular means. passage means, andinduce a rebounding of Patent No 3, 921, 290 Dated November 25, 1975Inventor s) Jay Richard Bailey It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 67,

Column 3, line 50, Column 7, line 54,

Column 8, line 53, Column 9, line 38,

Column 12, Column 13, Column 14,

Column 16,

Column 1 7,

Column 1 8,

Column 18, Column 23,

[SEAL] beiorel'stated" change "hertofore" to .heretofore after'means"insert and after "the" change "aforsaid" to aforesaid after"opening" insert in after "to delete "a".

line 64, before "interior" insert and line 45, after "passage change"meand" to means line 12, after "means" delete the comma and after "8"insert a comma line 63, after "and" add the following:

support means, including said outlet passage means, telescopinglymounting said flow restricting means for substantially unimpeded cyclicmovement. line 10, before "improvement" insert the line 31, before"means" change "restriction" to restitution line 64 after "piston"change "said" to and line 9, after "annular" insert passage Signed andScaled thus twenty-fifth Day Of May Attest:

C. MARSHALL DANN Commissioner of Parents and Trqdemarks f RUTH c. MASONArresting Officer UTED STATES PATENT OFFICE QE'HMCATE 0F CORRECTIONPatent No. 3, 921, 290 Dated November 25, 1975 Inventor(s) Jay RichardBailey It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 1, line 67, before "stated" change "hertofore" to heretoforeColumn 3, line 50, after "means" insert and Column 7, line 54, after"the" change "aforsaid' to aforesaid Column 8, line 53, after "opening"insert in Column 9, line 38, after "to" delete "a".

Column 12, line 64, before "interior" insert and Column 13, line 45,after "passage" change "meand" to means Column 14, line 12, after"means' delete the comma and after "8" insert a comma Column 16, line63, after "and" add the following:

support means, including said outlet passage means, telescopinglymounting said flow restricting means for substantially unimpeded cyclicmovement.

Column 17, line 10, before "improvement" insert the Column 18, line 31,before "means" change "restriction" to restitution Column 18, line 64after "piston" change "said" to and Column 23, line 9, after "annular"insert passage Saigncd and Scaled this twenty-fifth Day of May 1976[SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parentsand Trademarks

1. In a chain saw including an apparatus for reducing the noisegenerated by chain saw operation, and wherein said chain saw includeschain saw cutting means including guide bar means, and cutter chainmeans supported on said guide bar means for traversal through a cuttingpath; and chain saw power means including chain saw engine means havinga working chamber means, and chain saw power transmitting means operableto transmit driving force to said cutter chain means and cause saidcutter chain means to traverse said cutting path; the improvement insaid noise reducing apparatus comprising: exhaust passage meanscommunicating with said working chamber means of said chain saw enginemeans and operable to transmit a flow of cyclically pulsing exhaust gastherefrom; generally tubular, outlet passage means operable to receivesaid flow of exhaust gas and transmit said flow to the atmosphere;exhaust flow responsive, cyclically operable flow restricting meanstelescopingly mounted in said outlet passage means and operable inresponse to pressure pulsations in said flow of exhaust gas tocyclically restrict a portion of said flow of exhaust gas transmittedthrough said outlet passage means; continuously operable venting meansoperable to permit a continuous flow of a portion of said flow ofexhaust gas through said outlet passage means to the atmosphereconcurrent with said cyclic restriction of a portion of said exhaustflow through said outlet passage means; and
 2. In a chain saw includingan apparatus for reducing the noise generated by chain saw operation,and wherein said chain saw includes chain saw cutting means includingguide bar means, and cutter chain means supported on said guide barmeans for traversal through a cutting path; and chain saw power meansincluding chain saw engine means having a working chamber means, andchain saw power transmitting means operable to transmit driving force tosaid cutter chain means and cause said cutter chain means to traversesaid cutting path; improvement in said noise reducing apparatuscomprising: exhaust passage means communicating with said workingchamber means of said chain saw engine means and operable to transmit aflow of cyclically pulsing exhaust gas therefrom; surge chamber meansoperable to Receive said flow of exhaust gas from said exhaust passagemeans; acoustic filter means including generally tubular means includinglateral wall means defining interior passage means communicating withthe atmosphere and extending within said surge chamber means, andtransverse passage means intersecting said lateral wall means of saidgenerally tubular means and providing restricted, acoustic filtering,fluid communication between said surge chamber means and the interiorpassage means of said generally tubular means; flow restricting meansmounted in said generally tubular means and operable to cyclicallyrestrict at least a portion of said flow of exhaust gas; continuouslyoperable venting means operably associated with said generally tubularmeans and operable to maintain a continuously open flow path betweensaid surge chamber means and said atmosphere through which at least aportion of said flow of exhaust gas from said chain saw engine means maycontinuously pass; said noise reducing apparatus including a pluralityof assymetrically arranged tubular members defining baffle meanscontained within said surge chamber means and operable to baffle saidflow of exhaust gas within said surge chamber means between said exhaustpassage means and said acoustic filter means; said flow restrictingmeans being telescopingly associated with said tubular means andsupported by said noise reducing apparatus for substantially unimpededreciprocating movement relative to said tubular means; said flowrestricting means including wall means telescopingly received with saidtubular means and operable to cooperate with said lateral wall means andinterior passage means of said tubular means and define generallyannular passage means within said interior passage means operable todeflect a flow of exhaust gas passing transversely of said lateral wallmeans through said transverse passage means and cause said deflectedflow of exhaust gas to flow generally longitudinally of said interiorpassage means; said continuously operable venting means comprisinggenerally central venting passage means extending generally centrallyand longitudinally of each of said flow restricting means and saidannular passage means, with said venting passage means being defined byand carried by said flow restricting means; said generally annularpassage means providing fluid communication between said generallycentral, venting passage means and said surge chamber means; saidgenerally annular passage means being operable to provide fluidcommunication, independent of said generally central venting passagemeans, between said atmosphere and said surge chamber means; said flowrestricting means including generally annular, flow restricting wallmeans extending transversely of said generally annular passage means andcyclically operable in response to said flow of exhaust gas tocyclically restrict a portion of said annular passage meanscommunicating with said atmosphere, with said generally annular wallmeans being operable to move away from said annular passage means andtend to reduce restriction of said generally annular passage means andoperable to move toward said annular passage means and increaserestriction of said generally annular passage means; said noise reducingapparatus further including flow deflecting means providing exhaust gasdeflecting, fluid communication between said flow of exhaust gas issuingfrom said interior passage means and said atmosphere, said flowdeflecting means including restriction means operable to be impacted bysaid flow restricting means, when said generally annular wall means ismoving away from said annular passage means and tending to reduce therestriction of said generally annular passage means, and induce arebounding of said flow restricting means tending to move said generallyannular wall means toward said annular passage means and induce anincrease in restricting of said generallY annular passage means; saidtransverse passage means of said acoustic filter means including a firstplurality of elongate openings extending longitudinally of saidgenerally annular passage means, spaced circumferentially about saidgenerally tubular means, and operable to discharge exhaust gas directlyinto said generally annular passage means, and a second plurality ofelongate openings comprising a portion of said continuously operableventing means and operable to discharge exhaust gas into said interiorpassage means without passage through said generally annular passagemeans.
 3. In a chain saw including an apparatus for reducing the noisegenerated by an operating chain saw, wherein said chain saw includeschain saw cutting means including guide bar means, cutter chain meanssupported on said guide bar means for movement through a cutting plane;chain saw engine means including piston said cylinder means, crankshaftmeans driven by said piston means of said piston and cylinder means, andoperable to transmit driving force to said cutter chain means; saidnoise reducing apparatus comprising: conduit means operable to transmitcyclically pulsing exhaust fluid from said cylinder means of said pistonand cylinder means; surge chamber means, said surge chamber means beingoperable to receive exhaust fluid from said conduit means; acousticfilter means including generally perforate, outlet passage definingmeans, said conduit means and said outlet passage defining means beingmutually offset, barrier means within said surge chamber means closing afirst end portion of said outlet passage defining means, outlet meansprovided by a second end of said outlet passage defining means, saidoutlet means being operable to transmit exhaust fluid to the exterior ofsaid surge chamber means, said outlet passage defining means including aplurality of openings providing communication between said outlet meansand the interior of said surge chamber means; a plurality of tubularbaffle means, said tubular baffle means being located within theinterior of said surge chamber means, said tubular baffle means beingmutually displaced and disposed nonsymmetrically in relation to saidoutlet passage defining means; and flow restricting means operable tocyclically restrict a flow of said exhaust fluid passing through saidacoustic filter means; continuously operable venting means operable topermit a continuous flow of at least a portion of a flow of said exhaustfluid through said acoustic filter means to the atmosphere; and supportmeans mounting said flow restricting means for substantially unimpededcyclic movement.
 4. In a chain saw including an apparatus for reducingthe noise generated by an operating chain saw, wherein said chain sawincludes chain saw cutting means including guide bar means, cutter chainmeans supported on said guide bar means for movement through a cuttingplane with said cutting plane being aligned in generally parallelrelation with a principal vibration plane of a chain saw; chain sawengine means including piston and cylinder means, crankshaft meansdriven by said piston means of said piston and cylinder means, andoperable to transmit driving force to said cutter chain means; and saidcrankshaft means being mounted for rotation about an axis of crankshaftrotation extending generally perpendicular to said principal vibrationplane; said noise reducing apparatus comprising: conduit means operableto transmit cyclically pulsing exhaust fluid from said cylinder means ofsaid piston and cylinder means, said conduit means having a longitudinalaxis extending generally parallel to said axis of crankshaft rotation;surge chamber means, said surge chamber means being operable to receiveexhaust fluid from said conduit means, said surge chamber means having ageNerally rectangular cross section extending generally parallel withsaid principal vibration plane; acoustic filter means includinggenerally perforate cylinder means having a longitudinal axis extendinggenerally parallel to said axis of crankshaft rotation, a longitudinal,generally central axis of said cylinder means being transverselydisplaced from a longitudinal, generally central axis of said conduitmeans, with said conduit means and said cylinder means being mutually,transversely offset, barrier means within said surge chamber meansclosing a first end portion of said cylinder means, outlet meansprovided by a second end of said cylinder means, said outlet means beingoperable to transmit exhaust fluid to the exterior of said surge chambermeans, said cylinder means including a plurality of generally radiallyopening and circumferentially spaced perforation means, said cutterchain means and chain saw engine means being operable to generatevibrations generally aligned with said principal vibration plane andacting on said cylinder means to generate vibrations therein directedgenerally transversely thereof and in general alignment with saidprincipal vibration plane; flow restricting means operable to cyclicallyrestrict a flow of said exhaust fluid passing through said acousticfilter means; continuously operable venting means operable to permit acontinuous flow of at least a portion of a flow of said exhaust fluidthrough said acoustic filter means to the atmosphere; and support meansmounting said flow restricting means for substantially unimpeded cyclicmovement.
 5. In a chain saw including an apparatus for reducing thenoise generated by an operating chain saw, wherein said chain sawincludes chain saw cutting means including guide bar means, cutter chainmeans supported on said guide bar means for movement through a cuttingplane, with said cutting plane being aligned in generally parallelrelation with a principal vibration plane of a chain saw; chain sawengine means including piston and cylinder means, crankshaft meansdriven by said piston means of said piston and cylinder means, andoperable to transmit driving force to said cutter chain means, saidcrankshaft means being mounted for rotation about an axis of crankshaftrotation extending generally perpendicular to said principal vibrationplane; said noise reducing apparatus comprising: conduit means operableto transmit cyclically pulsing exhaust fluid from said cylinder means ofsaid piston and cylinder means, said conduit means having a generallyrectangularly elongate cross section, and said conduit means having alongitudinal axis extending generally parallel to said axis ofcrankshaft rotation; surge chamber means, said surge chamber means beingoperable to receive exhaust fluid from said conduit means, said surgechamber means being supported on the exterior of said cylinder means,said conduit means extending from said surge chamber means and beingdirectly connected with the exterior of said cylinder means and disposedin direct, metal-to-metal engagement therewith, said surge chamber meanshaving a generally rectangular configuration including a generallyrectangular cross section extending generally parallel with saidprincipal vibration plane; acoustic filter means including generallyperforate cylinder means having a longitudinal axis extending generallyparallel to said axis of crankshaft rotation, a longitudinal, generallycentral axis of said cylinder means being transversely displaced from alongitudinal, generally central axis of said conduit means, with saidconduit means and said cylinder means being mutually, transverselyoffset, barrier means within said surge chamber means closing a firstend portion of said cylinder means, outlet means provided by a secondend of said second cylinder means, said outlet meaNs being operable totransmit exhaust fluid to the exterior of said surge chamber means, saidcylinder means including a plurality of generally radially opening andcircumferentially spaced perforation means, and said cutter chain meansand chain saw engine means being operable to generate vibrationsgenerally aligned with said principal vibration plane and acting on saidcylinder means to generate vibrations therein directed generallytransversely thereof and in general alignment with said principalvibration plane; a plurality of tubular baffle means, said tubularbaffle means being located within the interior of said surge chambermeans, each said tubular baffle means extending generally parallel tosaid axis of crankshaft rotation, and said tubular baffle means beingmutually displaced and spaced generally radially outwardly of saidcylinder means; said conduit means, said cylinder means, and saidtubular baffle means being generally mutually parallel and subject tosaid vibrations generated in general alignment with said principalvibration plane; flow restricting means operable to cyclically restricta flow of said exhaust fluid passing through said acoustic filter means;continuously operable venting means operable to permit a continuous flowof at least a portion of a flow of said exhaust fluid through saidacoustic filter means to the atmosphere; and support means mounting saidflow restricting means for substantially unimpeded cyclic movement.
 6. Anoise reducing apparatus for a cyclic, internal combustion engine, saidapparatus comprising: exhaust passage means operable to communicate witha working chamber means of cyclic, internal combustion engine means andoperable to transmit a flow of cyclically pulsing exhaust gas therefrom;generally tubular, outlet passage means operable to receive said flow ofexhaust gas and transmit said flow to the atmosphere; exhaust flowresponsive, cyclically operable, flow restricting means telescopinglymounted in said outlet passage means and operable in response topressure pulsations in said flow of exhaust gas to cyclically restrict aportion of said flow of exhaust gas transmitted through said outletpassage means; continuously operable venting means operable to permit acontinuous flow of a portion of said flow of exhaust gas through saidoutlet passage means to the atmosphere concurrent with said cyclicrestriction of a portion of said exhaust gas flow through said outletpassage means; and support means including said outlet passage means,telescopingly mounting said flow restricting means for substantiallyunimpeded cyclic movement.
 7. In a chain saw including an apparatus forreducing the noise generated by chain saw operation, and wherein saidchain saw includes chain saw cutting means including guide bar means,and cutter chain means supported on said guide bar means for traversalthrough a cutting path; and chain saw power means including chain sawengine means having a working chamber means, and chain saw powertransmitting means operable to transmit driving force to said cutterchain means and cause said cutter chain means to traverse said cuttingpath; the improvement in said noise reducing apparatus comprising:exhaust passage means communicating with said working chamber means ofsaid chain saw engine means and operable to transmit a flow ofcyclically pulsing exhaust gas therefrom; surge chamber means operableto receive said flow of exhaust gas from said exhaust passage means;acoustic filter means including generally tubular means includinglateral wall means defining interior passage means communicating withthe atmosphere and extending within said surge chamber means, andtransverse passage means intersecting said lateral wall means of saidgenerally tubular means and providing restricted, acoustic filtering,fluid communication between said surge chamber means and the interiorpassage means of said generally tubular means; flow restricting meansmounted in said generally tubular means and operable to cyclicallyrestrict at least a portion of said flow of exhaust gas; andcontinuously operable venting means operably associated with saidgenerally tubular means and operable to maintain a continuously openflow path between said surge chamber means and said atmosphere throughwhich at least a portion of said flow of exhaust gas from said chain sawengine means may continuously pass; said flow restricting means beingtelescopingly associated with said tubular means and supported by saidnoise reducing apparatus for substantially unimpeded reciprocatingmovement relative to said tubular means; said flow restricting meansincluding wall means telescopingly received with said tubular means andoperable to cooperate with said lateral wall means and interior passagemeans of said tubular means and define generally annular passage meanswithin said interior passage means; said continuously operable ventingmeans comprising generally central venting passage means extendinggenerally centrally and longitudinally of each of said flow restrictingmeans and said annular means, with said venting passage means beingdefined by and carried by said flow restricting means; said generallyannular passage means providing fluid communication between saidgenerally central, venting passage means and said surge chamber means;said generally annular passage means being operable to provide fluidcommunication, independent of said generally central venting passagemeans, between said atmosphere and said surge chamber means; and saidflow restricting means including generally annular, flow restrictingwall means extending transversely of said generally annular passagemeans and cyclically operable, in response to said flow of exhaust gas,to cyclically restrict a portion of said annular passage meanscommunicating with said atmosphere, with said generally annular wallmeans being operable to move away from said annular passage means andtend to reduce restriction of said generally annular passage means andoperable to move toward said annular passage means and increaserestriction of said generally annular passage means.
 8. In a chain sawincluding an apparatus for reducing the noise generated by chain sawoperation, and wherein said chain saw includes chain saw cutting meansincluding guide bar means, and cutter chain means supported on saidguide bar means for traversal through a cutting path; and chain sawpower means including chain saw engine means having a working chambermeans, and chain saw power transmitting means operable to transmitdriving force to said cutter chain means and cause said cutter chainmeans to traverse said cutting path; the improvement in said noisereducing apparatus comprising: exhaust passage means communicating withsaid working chamber means of said chain saw engine means and operableto transmit a flow of cyclically pulsing exhaust gas therefrom; surgechamber means operable to receive said flow of exhaust gas from saidexhaust passage means; acoustic filter means including generally tubularmeans including lateral wall means defining interior passage meanscommunicating with the atmosphere and extending within said surgechamber means, and transverse passage means intersecting said lateralwall means of said generally tubular means and providing restricted,acoustic filtering, fluid communication between said surge chamber meansand the interior passage means of said generally tubular means; flowrestricting means mounted in said generally tubular means and operableto cyclically restrict at least a portion of said flow of exhaust gas;and continuously operable venting means operably associated with saidgenerally tubular means and operable to maintain a continuously openflow path between said surge cHamber means and said atmosphere throughwhich at least a portion of said flow of exhaust gas from said chain sawengine means may continuously pass; said noise reducing apparatusincluding baffle means contained within said surge chamber means andoperable to baffle said flow of exhaust gas within said surge chambermeans between said exhaust passage means and said acoustic filter means;said flow restricting means being telescopingly associated with saidtubular means and supported by said noise reducing apparatus forsubstantially unimpeded reciprocating movement relative to said tubularmeans; said flow restricting means including wall means telescopinglyreceived with said tubular means and operable to cooperate with saidlateral wall means and interior passage means of said tubular means anddefine generally annular passage means within said interior passagemeans operable to deflect a flow of exhaust gas passing transversely ofsaid lateral wall means through said transverse passage means and causesaid deflected flow of exhaust gas to flow generally longitudinally ofsaid interior passage means; said continuously operable venting meanscomprising generally central venting passage means extending generallycentrally and longitudinally of each of said flow restricting means andsaid annular passage means, with said venting passage means beingdefined by and carried by said flow restricting means; said generallyannular passage means providing fluid communication between saidgenerally central, venting passage means and said surge chamber means;said generally annular passage means being operable to provide fluidcommunication, independent of said generally central venting passagemeans, between said atmosphere and said surge chamber means; said flowrestricting means including generally annular, flow restricting wallmeans extending transversely of said generally annular passage means andcyclically operable in response to said flow of exhaust gas tocyclically restrict a portion of said annular passage meanscommunicating with said atmosphere, with said generally annular wallmeans being operable to move away from said annular passage means andtend to reduce restriction of said generally annular passage means andoperable to move toward said annular passage means and increaserestriction of said generally annular passage means; and said noisereducing apparatus further including flow deflecting means providingexhaust gas deflecting, fluid communication between said flow of exhaustgas issuing from said interior passage means and said atmosphere, saidflow deflecting means including restitution means operable to beimpacted by said flow restricting means, when said generally annularwall means is moving away from said annular passage means and tending toreduce the restriction of said generally annular passage means, andinduce a rebounding of said flow restricting means tending to move saidgenerally annular wall means toward said annular passage means andinduce an increase in restricting of said generally annular passagemeans.